1. Field of the Invention
This invention relates to an artificial knee joint, and more particularly to an artificial knee joint that includes a push rod biased to rotate a prosthetic lower leg rapidly to align with a residual thigh.
2. Description of the Related Art
Referring to FIGS. 1 and 2, a conventional artificial knee joint 200 is shown to include a joint seat 80, two links 81 (only one is shown), a support frame 82, and a hydraulic device 83. The joint seat 80 is connected fixedly to a thigh 8 of the prosthesis wearer, and is connected rotatably to the support frame 82 by the links 81. The hydraulic device 83 includes a cylinder body 830 that has upper and lower oil chambers 832, 833, and a piston rod 831 that is connected to the links 81 and that is movable within the cylinder body 830. The upper and lower oil chambers 832, 833 are in fluid communication with each other via an oil passage 834. As such, the hydraulic device 83 can retard relative rotation of the thigh 8 and the lower leg 9 during extension and flexion of the artificial knee joint 200.
When the thigh 8 is raised to flex the joint 200, as shown in FIG. 1, a coiled compression spring 835 is compressed by the piston rod 831. Subsequently, when the thigh 8 is turned frontwardly to align the thigh 8 with the lower leg 9, as shown in FIG. 2, the coiled compression spring 835 returns to its stretched state. Although the coiled compression spring 835 can push the piston rod 831 upwardly so as to bias the thigh 8 to align with the lower leg 9 during movement of the artificial knee joint 200 from the flexed position shown in FIG. 1 to the extended position shown in FIG. 2, the movement of the piston rod 831 is retarded due to presence of hydraulic liquid within the cylinder body 830 so that it takes a relatively long time to rotate the lower leg 9 relative to the thigh 8 from the position shown in FIG. 1 to that shown in FIG. 2. As such, the lower leg 9 may not be able to align with the thigh 8 when the lower leg 9 is pressed against the ground by the thigh 8 during fast walking, there by resulting in falling of the prosthesis wearer.